Braking assistance systems fitted in vehicles support the driver of the vehicle on hazard or emergency braking. The principle is based on analysis of accident events. In this analysis it was found that the possible brake force amplification was actually only rarely used, since the foot brake was activated either too weakly or too late. The result is a disadvantageous elongation of the braking distance, which may for example lead to collision accidents.
Conventional brake force boosters operate with an evacuated volume. The difference between the vacuum (negative pressure) and the atmospheric pressure is used to generate an auxiliary force. This serves to increase the activation force applied by the driver, so that the actual braking force is composed of the activation force and the auxiliary force. In contrast, electromechanical braking systems work without vacuum. Here the braking pressure is produced exclusively by one or more electric motors. Hence there is no mechanical connection between the brake pedal and the wheel brake(s). The resistance felt for example at the brake pedal is produced independently in the form of feedback.
The combination of electronic and usually hydraulic components entails certain inertia in the response behavior of such electromechanical braking systems. In other words, these require a reaction time between the deceleration request and the actual occurrence of the initiated braking process. To counter this disadvantage, in a parallel German application, number 10 2014 211 377.6, the applicant has proposed a method for operating an electromechanical braking system for a vehicle. This significantly improves the performance of the braking system as a whole, both for a deceleration request initiated by the person operating the vehicle and for an automatic vehicle control system. The entire content of German application number 10 2014 211 377.6 is incorporated herein by reference.
The solution proposed provides that, in advance of a possible braking process, on the basis of a trigger factor, a temporary pre-pressure is created in at least one part of the vehicle braking system. In this way, when the expected braking process actually occurs, a pre-pressure created semi-preventatively is already present to an adequate level. During the actual braking process, the pre-pressure may be passed on, either in full or in part, to at least one wheel brake of the vehicle braking system. The pre-pressure may evidently also be supplemented by an additional pressure depending on the intensity of the braking process. As a result, the reaction time of the braking system is significantly reduced.
Despite the resulting advantages, electromechanical braking systems still offer room for improvement. Thus in connection with the creation of pre-pressure, the question arises of how this can be adapted ideally to the individual deceleration request.